In oil field operations where earth formations are traversed by a casing it is customary to produce perforations at selected intervals along the casing where the perforations extend from the casing, through a surrounding cement sheath and into the earth formations. The perforations serve to place the bore of the casing and the earth formations in fluid communications for either injecting liquids into the formations or for producing fluids from the formations.
Typical completion practices for producing perforations currently utilize shaped charges. Shaped charges, when detonated, produce a perforating jet of high velocity, high energy particulate matter which penetrate a steel casing, a column of cement and earth formations to produce a perforation. While there are a number of shaped charge designs to eliminate the side effects of a perforating jet, there is no effective way to eliminate damage to the earth formations by the perforating jet or damage to the perforation. The damage includes plugging of the earth formation or the perforation by either the perforating jet or a jet slug. While some jet slugs can be caught or principally eliminated by design, the damage to the wall of the perforation cannot be eliminated.
To enhance the flow characteristics, it has been proposed to "back-flush" the perforations by a pressure differential between the formations and the casing so that the effects of the jet perforation can be flushed out of or from the earth formations. However, the effectiveness of this process is subject to adequate formation pressure and permeability.
In the prior art, efforts were made to develop perforations by a hydraulic jet of fluid using surface pumps, and this process was never widely used although it was appreciated that a high velocity fluid jet could effectively produce perforations.
Both shaped charge perforating and hydraulic perforating as currently done, have limited penetration depth into the formation from the well bore. Deeper penetration is desirable for increased well production.